Resolve "Adhoc storage deployment needs to be refactored"

This MR implements a generic mechanism for deploying adhoc storage
systems in `scord-ctl`. The mechanism allows users to define via
the `scord-ctl.conf` configuration file which scripts should be 
used to start and stop an adhoc storage system.

Closes #116

See merge request !93

- Reason: There are issues with `std::ranges` implementation in
clang-10, clang-11, and clang-12 (at least).

- Refactor `eval()`: The function now returns a new `command` instance.
- Add `as_vector()`: This function splits the command line by ' ' and
returns it as a vector of strings.

- Implement `environment::as_vector()`.
- Add `environment::size()`.

Merge branch 'amiranda/115-adhoc-storage-deployment-needs-to-be-executed-by-scord-ctl-instead-of-scord' into 'main'

Resolve "Adhoc storage deployment needs to be executed by `scord-ctl` instead of `scord`"

Closes #115

See merge request !92

`scord` now just forwards the request to the appropriate `scord-ctl`
instance.

- Add `endpoint lookup(std::string address)` so that a RPC server can
lookup peers for RPC forwarding.
- Add `std::string self_address()` so that a RPC server can determine
its own address string.

Our network interface now relies on Thallium's support for `providers`
(https://mochi.readthedocs.io/en/latest/thallium/09_providers.html).
This allows using the member functions from a class as RPC handlers,
which in turn allows RPC handers to access the class' data members.

Thus, we have heavily refactored `scord`:

- Create a new `scord::rpc_server` class that inherits both from
`network::server` and `network::provider`. This enables the
aforementioned functionality.
- The RPC handlers for `scord` are now member functions of
`scord::rpc_server` instead of free functions.
- The managers used by `scord` (i.e. the `job_manager`,
`adhoc_storage_manager`, and `pfs_storage_manager` are now members of
`scord::rpc_server` instead of singletons, since they no longer need to
be accessed globally.

Similarly for `scord-ctl`:
- Create a new `scord_ctl::rpc_server` class that inherits both from
`network::server` and `network::provider`. This enables the
aforementioned functionality.
- The RPC handlers for `scord-ctl` are now member functions of
`scord_ctl::rpc_server` instead of free functions.

Additionally, we have also moved the `network` and `logger` namespaces
outside of `scord`, since this code is shared by both `scord` and
`scord-ctl`.

Update tests to start scord-ctl as needed

Fixes #129

Fixes #128

Resolve "Refactor CLI for scord and scord-ctl"

Closes #127

See merge request !91

scord:
- Configuration file now uses standard YAML format
- Add `--output` CLI argument (SCORD_LOG_OUTPUT)

scord-ctl:
- Add `--output` CLI argument
- Add `--listen` CLI argument (Fixes #126)
- Remove configuration file

Both:
- Remove file_options dependency
- Remove genopts dependency
- Replace yaml-cpp with rapidyaml
- Replace general settings with specific configurations (fixes #20)
- General improvements and bugfixes in `logger`
- Improved `net::server` configuration
- Fix fork()-related bug in `signal_listener`
- Remove environment variables

"Resolve build fails with outdated `tl::expected`"

See merge request !89

Fixes #125

Merge branch 'amiranda/93-api-offers-no-way-to-tear-down-an-adhoc-storage-system-after-it-has-been-deployed' into 'main'

Resolve "API offers no way to tear down an adhoc storage system after it has been deployed"

Closes #93

See merge request !87

Resolve "Build with Clang"

Closes #121

See merge request !86